Inflammation is a response of vascularized tissues to infection or injury and is affected by adhesion of leukocytes to the endothelial cells of blood vessels and their infiltration into the surrounding tissues. In normal inflammation, the infiltrating leukocytes release toxic mediators to kill invading organisms, phagocytize debris and dead cells, and play a role in tissue repair and the immune response. However, in pathologic inflammation, infiltrating leukocytes are over-responsive and can cause serious or fatal damage. See, e.g., Hickey, Psychoneuroimmunology II (Academic Press 1990).
The integrins are a family of cell-surface glycoproteins involved in cell-adhesion, immune cell migration and activation. Alpha-4 integrin is expressed by all circulating leukocytes except neutrophils, and forms heterodimeric receptors in conjunction with either the beta-1 (β1) or beta-7 (β7) integrin subunits; both alpha-4 beta-1 (α4β1) and alpha-4 beta-7 (α4β7) play a role in migration of leukocytes across the vascular endothelium (Springer et al., Cell 1994, 76: 301-14; Butcher et al., Science 1996, 272: 60-6) and contribute to cell activation and survival within the parenchyma (Damle et al., J. Immunol. 1993; 151: 2368-79; Koopman et al., J. Immunol. 1994, 152: 3760-7; Leussink et al., Acta Neuropathol. 2002, 103: 131-136). α4β1 is constitutively expressed on lymphocytes, monocytes, macrophages, mast cells, basophils and eosinophils.
Alpha-4 beta-1 (also known as very late antigen-4, VLA-4), binds to vascular cell adhesion molecule-1 (Lobb et al., J. Clin. Invest. 1994, 94: 1722-8), which is expressed by the vascular endothelium at many sites of chronic inflammation (Bevilacqua et al., 1993 Annu. Rev. Immunol. 11: 767-804; Postigo et al., 1993 Res. Immunol. 144: 723-35). α4β1 has other ligands, including fibronectin and other extracellular matrix (ECM) components.
The alpha-4 beta-7 dimer interacts with mucosal addressin cell adhesion molecule (MAdCAM-1), and mediates homing of lymphocytes to the gut (Farstad et al., 1997 Am. J. Pathol. 150: 187-99; Issekutz, 1991 J. Immunol. 147: 4178-84). Expression of MAdCAM-1 on the vascular endothelium is also increased at sites of inflammation in the intestinal tract of patients with inflammatory bowel disease (IBD) (Briskin et al., 1997 Am. J. Pathol. 151: 97-110).
Adhesion molecules such as alpha-4 integrins are potential targets for therapeutic agents. For instance, the VLA-4 receptor of which alpha-4 integrin is a subunit is an important target because of its interaction with a ligand residing on brain endothelial cells. Diseases and conditions resulting from brain inflammation have particularly severe consequences. In another example, the alpha-4 beta-7 integrin dimer is an important target due to its involvement in lymphocyte homing and pathological inflammation in the gastrointestinal tract.
Alpha-4 beta-1 integrin is expressed on the extracellular surface of activated lymphocytes and monocytes, which have been implicated in the pathogenesis of acute inflammatory brain lesions and blood brain barrier (BBB) breakdown associated with multiple sclerosis (MS) (Coles et al., 1999 Ann. Neurol. 46(3): 296-304). Agents against alpha-4 integrin have been tested for their anti-inflammatory potential both in vitro and in vivo. See Yednock et al., Nature 1992, 356: 63-66; U.S. Pat. No. 5,840,299 to Bendig et al., issued Nov. 24, 1998, and U.S. Pat. No. 6,001,809 to Thorsett et al., issued Dec. 14, 1999. The in vitro experiments demonstrate that alpha-4 integrin antibodies block attachment of lymphocytes to brain endothelial cells. Experiments testing the effect of alpha-4 integrin antibodies on animals having the artificially induced condition simulating multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), have demonstrated that administration of anti-alpha-4 integrin antibodies prevents inflammation of the brain and subsequent paralysis in the animals. Collectively, these experiments identify anti-alpha-4 integrin antibodies as potentially useful therapeutic agents for treating multiple sclerosis and other inflammatory diseases and disorders.
To date, no therapies have been discovered which inhibit or prevent demyelination let alone agents that promote remyelination. For example, multiple sclerosis impacts human health and costs for maintaining health more than any other demyelinating disease. No effective treatment exists for MS. It is a disease that afflicts primarily young adults (i.e., mean age of 30) with an incidence of 1 case per 1,000 individuals. Experimental autoimmune encephalomyelitis is the major animal model used for studying MS. However, unlike with EAE, MS is an autoimmune disease with an unknown cause. Disease progression is characterized by an influx of immune cells into the central nerve system that eventually results in edema, demyelination, axonal damage and loss.
New compounds, compositions and methods for using these compounds and compositions to inhibit demyelination, to promote remyelination and/or treat paralysis associated with demyelination are needed and continue to be sought out for the treatment of diseases such as MS, as well as other demyelinating diseases linked with inflammation.